A = A. Established as an axiom so that we cannot have 'A = not-A'. Thus when we say 'A is B' we can try to falsify the null hypothesis by attempting to demonstrate that 'B is not-A'. Failure to do so increase our confidence that 'A is B', which we could not do without the underpinning of 'A is A' which implies 'A is not not-A'.
I have no studies in philosophy or logic so I have to wonder if I just spoke out of an unpopular orifice.